Conditional dormancy of Stipa lagascae (Poaceae) bulk-harvested on seed increase plots in South Tunisia: a reassessment and a surprise

Background and aims – With the perspective to reseed degraded drylands, grass seeds are often stocked for several years. This common practice overlooks conditional dormancy and the necessity to preserve it. This paper reports on the germination ecology of Stipa lagascae Roem. & Schult., which is a circum-Mediterranean winter-growing bunch grass of high grazing value. However, the published record on its germination ecology is scarce and inconsistent.Methods – This record was reassessed through a series of germination trials in combination with dormancy breaking treatments on seeds that were mainly harvested on a seed increase plot in South-Tunisia.Key results –The surprise finding was that Stipa lagascae exhibits a particular kind of conditional dormancy for many months after harvest. Whereas dormant seeds barely germinate at 10°C in classical Petri dishes or on germination tables, they germinate massively (but not fully) when allowed full contact with a water-saturated substrate at 7–10°C in boxes. Dehulling provokes fast germination of near 100% of the seeds, thus showing that the substrate effect at low temperatures breaks most but not all dormancy in a particular seed lot. This remaining or residual dormancy is not conditional, as it can only be broken through dehulling. There are thus two distinct germination windows: a very broad one for non-dormant seed and a narrow one for conditionally dormant seed.Conclusions – A pattern is suggested whereby each seed lot evolves through a continuum from full over conditional to non-dormancy and finally mortality. However, only the state of conditional dormancy times germination optimally with regard to the start of the winter growing season in South-Tunisia. Its ecological significance should be interpreted in combination with its trypanocarpy. Reseeding for restoration purposes and to render grazing value to depleted drylands should thus use conditionally dormant seed.

Grazing by large savanna herbivores indirectly alters ant diversity and promotes resource monopolisation

In savannas, grazing is an important disturbance that modifies the grass layer structure and composition. Habitat structural complexity influences species diversity and assemblage functioning. By using a combination of natural sites and manipulated experiments, we explored how habitat structure (grazing lawns and adjacent bunch grass) affects ant diversity and foraging behaviour, specifically the efficiency of resource acquisition, resource monopolisation and ant body size. We found that in the natural sites there was no difference in the amount of time ants took to locate resources, but in the manipulated experiments, ants were faster at locating resources and were more abundant in the simple treatments than in the more complex treatments. Ant body size was only affected by the manipulated experiments, with smaller ants found in the more complex treatments. In both the grazing lawn and bunch grass habitats there were differences in assemblage patterns of ants discovering resources and those dominating them. Seasonality, which was predicted to affect the speed at which ants discovered resources and the intensity of resource monopolisation, also played a role. We show that ants in winter monopolised more baits and discovered resources at a slower rate, but only at certain times within the experiment. Grazing in conjunction with season thus had a significant effect on ant diversity and foraging behaviour, with dominant ants promoted where habitat complexity was simplified when temperatures were low. Our results indicate that structural complexity plays a major role in determining ant assemblage structure and function in African savannas.

Pemanfaatan Tandan Kosong Sawit Dan Rumput Sebagai Bahan Kompos di PT Bukit Asam, Sumatera Selatan

PT Bukit Asam had strategies to improve soil fertility in the ex-mine land using compost. The amount of compost added to the soil depend on the extent of reclamation area. Oil palm empty fruit bunch and grass are highly potential to be used as the compost materials in reclamation area. The objectives of the research were to characterize the compost from oil palm empty fruit bunch and grass, and to compare the suitability between the result of this research and nasional standard compost. Oil palm empty fruit bunch and grass were obtained from PT Bumi Sawindo Permai and reclamation area of PT Bukit Asam, respectively. Composting site was located in the ex-mine land of PT Bukit Asam. Composting method used passively aerated static pile system. The results showed that the compost characteristic of oil palm empty fruit bunch compost had a dark yellowish brown color, pH at 9.3, C/N ratio at 14, and nutrients (C-Organic, N, P, K, and Mn Total). The compost characteristics of grass had a very dark brown, pH at 7.3, C/N ratio at 7, and nutrients (C-Organic, N, P, K, and Mn Total). The compost from oil palm empty fruit bunch and grass were in accordance with the national standard of compost.Keywords: empty fruit bunch, grass, compos

Phytocoenotic diversity and vegetation mapping of the Zaisan depression, Kazakhstan

The paper presents the results of vegetation studies in the Zaisan depression. The middle-scale vegetation map (s. 1 : 500 000) was created. Dominant species of vegetation cover form several ecological-physiognomic vegetation types: psammophytic shrub, psammophytic wormwood, psammophytic grass, perennial saltwort, sagebrush, shrub, saxaul, sagebrush – bunch grass, coniferous forest; floodplain meadow, shrub and woody are characteristic types of river valleys. These types are represented in the map legend. Analysis of the ecological preferences of the dominant species of Zaisan depression revealed the edaphic amplitude of plant species. A large part of dwarf semishrubs (sagebrushes and perennial saltworts) is characterized by wide edaphic amplitude. Shrub Spiraea hypericifolia has also a wide edaphic range. Stipa sareptana is the most ecologically labile species among bunch grasses. Zaisan saxaul is mainly grows on brown and gray-brown soils. The legend to the map is compiled on the base of zonal-typological principle, it contains 35 numbers. 8 numbers of the legend show the homogeneous vegetation, 27 – heterogeneous vegetation. Zonal types of vegetation occupy 64% of the territory (deserts – 32.4%, steppes – 31.6%); intrazonal vegetation – 23.6%. About 17% of the territory is agricultural lands, mostly located in the steppe zone.

A novel protocol for assessment of aboveground biomass in rangeland environments

Current methods to measure aboveground biomass (AGB) do not deliver adequate results in relation to the extent and spatial variability that characterise rangelands. An optimised protocol for the assessment of AGB is presented that enables calibration and validation of remote-sensing imagery or plant growth models at suitable scales. The protocol combines a limited number of destructive samples with non-destructive measurements including normalised difference vegetation index (NDVI), canopy height and visual scores of AGB. A total of 19 sites were sampled four times during two growing seasons. Fresh and dry matter weights of dead and green components of AGB were recorded. Similarity of responses allowed grouping into Open plains sites dominated by annual grasses, Bunch grass sites dominated by perennial grasses and Spinifex (Triodia spp.) sites. Relationships between non-destructive measurements and AGB were evaluated with a simple linear regression per vegetation type. Multiple regression models were first used to identify outliers and then cross-validated using a ‘Leave-One-Out’ and ‘Leave-Site-Out’ (LSO) approach on datasets including and excluding the identified outliers. Combining all non-destructive measurements into one single regression model per vegetation type provided strong relationships for all seasons for total and green AGB (adjusted R2 values of 0.65–0.90) for datasets excluding outliers. The model provided accurate assessments of total AGB in heterogeneous environments for Bunch grass and Spinifex sites (LSO-Q2 values of 0.70–0.88), whereas assessment of green AGB was accurate for all vegetation types (LSO-Q2 values of 0.62–0.84). The protocol described can be applied at a range of scales while considerably reducing sampling time.